libs/math/example/error_handling_example.cpp

// example_error_handling.cpp
// Copyright Paul A. Bristow 2007, 2010.
// Copyright John Maddock 2007.
// Use, modification and distribution are subject to the
// Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)
// Note that this file contains quickbook markup as well as code
// and comments, don't change any of the special comment markups!
// Optional macro definitions described in text below:
// #define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
// #define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
// #define BOOST_MATH_DOMAIN_ERROR_POLICY is set to: throw_on_error
//[error_handling_example
/*`
The following example demonstrates the effect of
setting the macro BOOST_MATH_DOMAIN_ERROR_POLICY
when an invalid argument is encountered. For the
purposes of this example, we'll pass a negative
degrees of freedom parameter to the student's t
distribution.
Since we know that this is a single file program we could
just add:
#define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
to the top of the source file to change the default policy
to one that simply returns a NaN when a domain error occurs.
Alternatively we could use:
#define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
To ensure the `::errno` is set when a domain error occurs
as well as returning a NaN.
This is safe provided the program consists of a single
translation unit /and/ we place the define /before/ any
#includes. Note that should we add the define after the includes
then it will have no effect! A warning such as:
[pre warning C4005: 'BOOST_MATH_OVERFLOW_ERROR_POLICY' : macro redefinition]
is a certain sign that it will /not/ have the desired effect.
We'll begin our sample program with the needed includes:
*/
#define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
// Boost
#include <boost/math/distributions/students_t.hpp>
using boost::math::students_t; // Probability of students_t(df, t).
// std
#include <iostream>
using std::cout;
using std::endl;
#include <stdexcept>
using std::exception;
#include <cstddef>
// using ::errno
/*`
Next we'll define the program's main() to call the student's t
distribution with an invalid degrees of freedom parameter,
the program is set up to handle either an exception or a NaN:
*/
int main()
{
cout << "Example error handling using Student's t function. " << endl;
cout << "BOOST_MATH_DOMAIN_ERROR_POLICY is set to: "
<< BOOST_STRINGIZE(BOOST_MATH_DOMAIN_ERROR_POLICY) << endl;
double degrees_of_freedom = -1; // A bad argument!
double t = 10;
try
{
errno = 0; // Clear/reset.
students_t dist(degrees_of_freedom); // exception is thrown here if enabled.
double p = cdf(dist, t);
// Test for error reported by other means:
if((boost::math::isnan)(p))
{
cout << "cdf returned a NaN!" << endl;
if (errno != 0)
{ // So errno has been set.
cout << "errno is set to: " << errno << endl;
}
}
else
cout << "Probability of Student's t is " << p << endl;
}
catch(const std::exception& e)
{
std::cout <<
"\n""Message from thrown exception was:\n " << e.what() << std::endl;
}
return 0;
} // int main()
/*`
Here's what the program output looks like with a default build
(one that *does throw exceptions*):
[pre
Example error handling using Student's t function.
BOOST_MATH_DOMAIN_ERROR_POLICY is set to: throw_on_error
Message from thrown exception was:
Error in function boost::math::students_t_distribution<double>::students_t_distribution:
Degrees of freedom argument is -1, but must be > 0 !
]
Alternatively let's build with:
#define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
Now the program output is:
[pre
Example error handling using Student's t function.
BOOST_MATH_DOMAIN_ERROR_POLICY is set to: ignore_error
cdf returned a NaN!
]
And finally let's build with:
#define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
Which gives the output show errno:
[pre
Example error handling using Student's t function.
BOOST_MATH_DOMAIN_ERROR_POLICY is set to: errno_on_error
cdf returned a NaN!
errno is set to: 33
]
*/
//] [error_handling_eg end quickbook markup]